Probably all the AHD veterans are happy enough with their old editions so as to not bother with the new version. Seems like somebody from Mayfair would chime in.

Many seem to like Alan Emrich's 3.1 living rules, I amongst them. I suspect that Alan's rules will be the de facto standard, regardless of what Mayfair does. Alan's got a tremendous amount of design and development experience, including his magnus opus Totaler Krieg (aka Axis Empires: Totaler Krieg).